1. Field of the Invention
The present invention relates to an alternator (AC generator) mounted on a vehicle such as a passenger car or a truck.
2. Description of Related Art
Recently, the engine noise of a vehicle such as a passenger car or a truck has been steadily reduced to meet the social demand for the reduction of vehicle noise, and also to increase merchantability of the vehicle. However, reducing the engine noise tends to make the noise of auxiliaries rotating at relatively high speeds which are mounted on the same vehicle, especially a vehicle-use alternator, more harsh and conspicuous.
There have been proposed various techniques for reducing the noise of a vehicle-use alternator, while improving the self-cooling capability of the vehicle-use alternator by making changes to the shape around cooling air discharge windows formed in a housing of the alternator. For example, Japanese Patent Application Laid-open No. 2000-69714 discloses smoothing a cooling air flow by streamlining ribs made so as to form cooling air discharge windows, to thereby reduce the drag force of the cooling air flow. Japanese Patent Application Laid-open No. 7-79543 discloses reducing the drag force of a cooling air flow by elaborating on the inclination of ribs around support members of a housing of a vehicle-use alternator.
However, the structures disclosed in the above described patent documents have a problem in that the fan noise of the vehicle-use alternator is not reduced much, because the reduction of the drag force of the cooling air flow around the ribs or the support members of the housing causes the cooling air flow to increase that much. In addition, although there occurs abrupt change in the cooling air flow at a boundary portion between the support member and the adjacent cooling air discharge window, that causes large wind pressure variation which can be a leading cause of the fan noise, no consideration on this is given in these documents.